1. Field of the Invention
The present invention relates to a signal generating circuit and a peak detection circuit, and more particularly to a signal generating circuit for detecting and comparing two different signals to produce either one of these signals, or alternatively a peak detection circuit for detecting a maximum or minimum signal output from a plurality of signal sources.
2. Brief Description of the Related Art
For example, the peak detection circuit for detecting a maximum or minimum signal output from a plurality of signal sources is used for adjustment of sensitivity of a video camera. FIG. 4 shows the construction of an example of a conventional peak detection circuit.
In FIG. 4, symbols S.sub.1 to S.sub.4 are signal sources, and the output signals from the sources are applied to each base of bipolar transistors Tr.sub.1 to Tr.sub.4. The emitters of transistors Tr.sub.1 to Tr.sub.4 are commonly connected to each other and also connected to a resistor R and an output buffer amplifier B.
In such a peak detection circuit, when a signal having the highest peak level is generated from any one signal source, the bipolar transistor associated therewith is turned on, a current flows through the resistor R to increase the level of the common line, and the transistors except the one to which the maximum peak level signal is applied is turned off. As a result, the output having the maximum peak value is detected by the buffer amplifier B.
However, when two or more transistors in the above described circuit are simultaneously turned on (for example, when signals having levels close enough are produced, two or more transistors are turned on), a further increased current flows through the resistor R to further raise the level of the common line, thereby the different peak value is detected even though the signals the same peak level value.